1. Field of the Invention
The present invention relates to a surface treatment solution for finely processing the surface of a glass substrate containing multiple ingredients. More specifically, the present invention relates to a surface treatment solution, useful for the fine surface processing of glass substrates, containing cation-yielding elements and their cation-yielding oxides, which is very profitably used for wet-etching/cleaning the surface of such glass substrates or etching/cleaning the surface of such glass substrates carrying finely fabricated semiconductor elements thereon during the fabrication of semiconductor devices.
2. Related Art
In the wet processing of glass panels for flat panel display devices, pattern-etching/cleaning of glass substrates containing cation-yielding elements and their cation-yielding oxides and purification/fine-processing of pattern-etched such glass substrates using an etching solution has been put into practice. Yet, demand for a technique enabling the more fine processing of glass substrates has become increasingly acute with the advent of more highly resolved display devices. For the fine surface processing of glass substrates which will serve as display panels, hydrofluoric acid (HF) or a mixture (buffered hydrofluoric acid (BHF)) of hydrofluoric acid (HF) and ammonium fluoride (NH4F) has been used as an important and indispensable agent for etching/cleaning glass substrates. However, demand for an etching agent enabling finer processing of glass substrates becomes manifest to further improve the performance and resolution of display devices.
Glass substrates to be used for the construction of liquid crystal (LC)-based or organic electroluminescence (EL)-based flat panel display devices have come to have an increasingly reduced thickness to meet the demand for more compact and power-saving display devices. In the manufacture of such glass substrates, however, the so-called mother glass plate has an increasingly larger size to improve the production efficiency and reduce the production cost. A glass substrate is obtained by thinning a mother glass plate.
However, the mechanical thinning of a mother glass plate has a limitation, because a mother glass plate must have strength sufficiently high enough to withstand stresses imposed during the thinning process. Therefore, if further thinning is required for a mechanically thinned glass plate (coarse glass substrate), the coarse glass substrate must be subjected to another kind of fine processing, e.g., chemical fine processing.
However, if a coarse glass substrate containing multiple ingredients, particularly cation-yielding elements and their oxides, is etched/cleaned by means of a conventional etching solution comprising HF or BHF, following two problems are encountered which interfere with the uniform etching/cleaning.
1) Crystals develop on the surface of a glass substrate and adhere thereto.
2) The surface of a glass substrate becomes significantly roughened after the treatment.
With regard to the problem 1), analysis of crystals adhered to the surface of a glass substrate revealed that it is composed of fluorides of cation-yielding elements contained in the glass substrate. Fluorides of cation-yielding elements have such a low solubility to HF and BHF as well as to water, that they are easily crystallized to adhere onto the surface of a glass substrate. The present inventors succeeded in reaching this finding for the first time.
The problem 2) was ascribed to that crystals developed on the surface of a glass substrate and adhered thereto interfere with etching and/or that cation-yielding elements and their oxides contained in a glass substrate are differently susceptible to etching, which causes the local variation in etching rate and etching amount. The present inventors succeeded in obtaining this knowledge for the first time.
The most important point of the technique for finely processing glass substrates is to uniformly process or treat glass substrates while preventing the occurrence of surface roughness.